Bis(fluoroalkyl)malononitriles and their preparation



United States Patent "in N 0 Drawing.

This invention relates to, and has as its main objects provision of, novel and useful dinitriles having fluoroalkyl substituents and a method for the preparation of the same.

A number of halogenated dinitriles are known, for ex ample, difiuoromalononitrile (French Patent 1,212,245), hexafluoroglutaronitrile [Chemical Abstracts 44,v 9475 f (1950)] and halogenated dinitriles of the formula HCXgCX (CN 2 wherein X represents a halogen (US. Patent 2,774,783). In accordance with the present invention, a new class of fluoroalkylrnalonom'triles has been prepared comprising bis(fiuoroalkyl)malononitriles of the formula wherein each R is selected from the group consisting of I perfluoroalkyl, chloroperfluoroalkyl and w-hydroperfiuoroalkyl having up to carbon atoms.

These bis(fluoroalkyl)malononitriles possess many properties both unusual and unexpected in comparison with the properties of the hitherto-known fluoroalkylnitriles. More particularly, the bis(fluoroalkyl)malononitriles of this invention undergo unexpected types of reactions with manycommon reagents. For example, di-

fluoromalononitrile reacts with water at 25 C. to form difluoromalonamlde,

F2 0 JJNH: 3

Ammonia also reacts with perfiuoroalkylnitn'les to form amidines.

The bis(fluoroalkyl)malononitriles of this invention also difier unexpectedly in their reactions with bases and thiols, in comparison with hitherto known perfluoroalkylnitriles. Thus, aqueous sodium hydroxide causes degradation of bis(trifluoromethy1)malononitrile to sodium fluoride whereas aqueous sodium hydroxide with perfluoroalkylnitriles yields the corresponding carboxylic acids. The difference in the behavior of the bis(fluoroalkyl)- carbon dioxide and acetone. alkyl)malononitrile can be isolated and purified by frac- 3,17%,949 Patentedl 'eh. 23,- 1965 malononitriles of this invention and perfiuoroalkylnitriles with tbiols is shown by the following equations:

EtsN' & a)2 )2 CHaSH LET-6 NO I 1-1 CHaSCN era The bis(fiuoroalkyl)malononitriles of this invention are prepared by pyrolyzing at 500900 C. a fluoroacyl cyanide dimer of the formula wherein R has the meaning defined above. Best results are obtained when the pyrolysis is carried out at temperatures between 600 and 700 C.; consequently this is the preferred pyrolysis temperature range. v

The pyrolysis is conveniently carried out at atmospheric pressure. However, subatmospheric or superatmospheric pressures can be employed if desired. It is also convenient to employ a stream of 'an inert carrier gas, e.g., nitrogen, to carry the fluoroacyl cyanide dimer through the heated reaction zone and to carry the pyrolysis products into the receiver. This use of an inert carrier gas is not/essential since carbon dioxide is formed as one of the pyrolysis products and this gas also facilitates transfer of the reactant and reaction products through the reaction zone.

The pyrolysis products leaving the reaction zone are collected in a receiver cooled to a low temperature, e.g., about C., by means of a. mixture of solid The resulting bis(fluorotional distillationin a conventional way.

The fiuoroacyl cyanide dimers used as starting materials in the process of this invention can be prepared from the corresponding fiuoroacyl chlorides and silver cyanide by the method described by R. H. Patton and I. H. Simons in J. Am. Chem. Soc. 77, 2016 (1955).

The products and process of this invention are illustrated in further detail in the nonlimiting examples which follow.

EXAMPLE I.BIS (TRIFLUOROMETHYL) MALONONITRILE 0 CN ON i 5 A I CF; O- -CF3 CF3(IICF3 CO; N ON A platinum tube inclined at an angle of about 25 with the horizontal is heated at 760 C. over a length of 12", and 10 ml. of trifluoroacetyl cyanide dimer is added dropwise over a period of one hour. A stream of nitrogen at a flow rate of about cc. per minute is passed through the tube during the addition. The reaction products are collected in a trap cooled by a mixture of solid carbon dioxide and acetone. The volatile material collected in the trap is transferred to a clean trap by simple distillation in vacuo. The liquid is then fractionally distilled and there is obtained about 4 ml. of a colorless liquid product boiling at 28-29 C. This product is identified as his (trifluoromethyDmalononitrile by infrared, nuclear magnetic resonance, and elemental analyses.

Analysis.Calcd for C F N C, 29.93%; F, 56.40%; N, 13.87%. Found: C, 30.23%; F, 56.34%; N, 13.28%.

When the procedure of Example I is repeated with chlorodifiuoroacetyl cyanide dimer and perfiuoropropionyl cyanide dimer substituted for trifluoroaoetyl cyanide diwhere R is as defined above. Other specific bis(fluoroalkyl)malononitriles are listed in the following Table I, together with the specific fluoroacyl cyanide dimers from which they are prepared.

Table I Fluoroacyl Cyanide Bis(fluoroalkyl)ma1ononitrile The products of this invention are useful for various purposes. They are especially useful as cyanating agents for mercaptans, whereby useful known thiocyanates can be'prepared by a simplified procedure. For example, methyl thiocyanate can be prepared as follows: A solution of 7.8 g. of bis(trifluoromethyl)malononitrile and ml. of methanethiol in ml. of anhydrous diethyl ether is stirred one hour at 0 C. Three drops of triethylamine is added and the reaction mixture stirred for 7 hours at room temperature in a reaction vessel fitted with a reflux condenser. The reaction mixture is then distilled, and, after removing a low boiling fraction there is obtive index ,n of 1.4618. This product is identified by proton magnetic resonance showing a single sharp resonance for CH S, and by an infrared absorption spectrum which is identical with the spectrum of an authentic specimen of methyl thiocyanate. The resulting thiocyanates are useful for the same purpose as the commercially available alkyl thiocyanates, and this process avoids the usual multiple step methods for preparing such thiocyanates.

Since obvious modifications and equivalents in the invention will be evident to those skilled in the chemical arts, I propose to be bound solely by the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A bis(fluoroalkyl)malononitrile of the formula II (RXCCNM wherein R is selected from the group consisting of perfiuoroalkyl, chloroperfluoroalkyl and w-hydroperfluoroalkyl of up to 10 carbons. V

4. The process of preparing bis(trifluoromethyl)malononitrile which comprises pyrolyzing trifluoroacetyl cyanide dimer at a temperature of about 500-900 C.

7 References Cited in the file of this patent UNITED STATES PATENTS 2,774,783 Ardis Dec. 18, 1956 

1. A BIS(FLUOROALKYL)MALONONITRILE OF THE FORMULA 